The present invention has for object a device for the control of a sequential burner of a cooking apparatus.
In cooking equipment it is known to produce burners called "sequential," that is to say functioning intermittently or in sequences. Such a type of operation permits of metering the consumed heating energy by regulating a predetermined time of feed of the burner, for a given cooking operation. Thus the ratio of the time of operation or feeding to the total time of the cycle expresses the metering of the energy as a percentage.
To facilitate the use of a burner equipped with a control device of this kind it must be possible to mark up fixed sequences between a minimum and a maximum, and to permit intermediate adjustments. Hitherto the known control devices are of three types:
programmer device PA1 energy metering device PA1 electronic device.
By reason of their bulk, programmers permit of realising only a certain number of fixed sequences, without possibility of intermediate adjustments.
The energy metering devices currently called "infinites" are realised in such manner as periodically to eliminate the electric feed of a resistor in such manner that the ratio of the operating time to the total cycle time is identical for all cycles, for a specific position of the adjusting knob. The driving element of an "infinite" is a bimetallic strip heated by a resistor connected after the contact; when the elastic force of the bimetallic strip deformed by the rise in temperature becomes greater than the attraction force of a magnet, the contact opens sharply, and the same applies on re-engagement. The metering variation is obtained by means of a cam fixing the initial position of the bimetallic strip.
Such an energy metering device permits of effecting a continuous adjustment of the energy supply, by variation of the angular position of the cam, it thus being possible to obtain fixed sequences and intermediate adjustments at the choice of the user. Unfortunately it has been observed that these sequences are subject to undesirable variations, and it has been determined that these variations derived from the following reasons: the variation of the tension of the supply mains, the variations of the heating resister of the thermal switch when the metering device is manufactured on a large scale, and the variation of the force of the permanent magnet associated with the thermal switch.
Under these circumstances the object is not achieved of obtaining a control device having satisfactory operation and reliability. The electronic device has the drawback of being destroyed if the temperature rises.
The invention has the aim of realising a control device which has only reduced bulk, which permits intermediate adjustments between the fixed sequences and which does not display the drawbacks of the energy metering systems.
To this end and in accordance with the invention the control device of at least one sequential burner of a cooking apparatus comprises a geared-down synchronous motor and a drum which can be driven in rotation by this motor, and the drum co-operates with at least one electric contact pressing upon the surface of the drum and is provided with at least one electrically conductive track formed in such manner as to permit operation of the burner in accordance with heating sequences which are variable as a function of the position of the electric contact upon the drum, means being provided to regulate this position of the contact in relation to the conductive track in order that the duration of the heating sequences of the burner may be varied progressively and continuously.
This device is of only slight bulk in comparison with programmers, and the geared-down synchronous motor is not sensitive to variations in the mains voltage, in contrast to the energy metering device.
According to one particular feature of the invention the electrically conductive track is staged in order to present to the burner feed electric contact a length variable as a function of the position of the contact on the drum.
As the position of the sliding contact is controlled either by a linear slider or by a rotating knob, thus the user can adjust the heating sequence to the desired value by suitably positioning the contact on the track of the drum in order that the burner may be fed only when contact is established between the electric track and the said contact.
According to one form of embodiment of the invention the drum is cylindrical and comprises a conductive track of width increasing preferably practically continuously in the axial direction of the drum, this track terminating in a conductive band extending over the whole circumference of the drum, while an interval is reserved between the narrowest extremity of the track and the corresponding terminal part of the drum, in order to constitute a non-conductive band extending over the whole circumference of the drum.
Thus the user has the facility of displacing the adjustment contact between a zero point where the various elements of the device are electrically disconnected and a non-sequenced operating point, a whole series of intermediate sequences, the durations of which are variable at the choice of the user, being available between these two extreme points.
Thus the invention solves the problem in a particularly simple manner, and no undesirable variation of resistance or of permanent magnet force can intervene in this system.
According to a further characteristic of the invention the control device comprises a system for ignition and feeding of the burner at the commencement of each heating sequence, also a flame presence security device co-operating with the ignition and feed system so as automatically to cut off the gas supply of the burner after a predetermined time if the ignition system should fail to function or should function defectively.
This form of embodiment has the purpose of bringing a positive security to the control device in order to ensure an automatic interruption of the gas feed to the burner after a predetermined duration in different hypothetical cases which will be explained hereinafter.
According to one form of embodiment of the invention the safety device comprises means for keeping open a burner gas feed electric valve in the presence of a flame at the burner for the said predetermined time during which a first contact of the ignition and feed system, controlled by the rotation of the drum, is open.
According to one important characteristic of the invention the ignition and feed system of the burner comprises a cam fixed to the end of the drum which opens the said first contact after the closure of a second contact at the commencement of a heating sequence, and during the said predetermined time, these two contacts being placed on the terminals of the electric valve and of the drum drive motor, and the electric valve and the motor are connected to a third reversing contact of the safety device which, when a flame appears at the burner, comes into a position in which it permits continuity of the electric feed of the motor and of the opening of the electric valve through the duration of opening of the first contact, then the cam recloses this first contact, permitting the drum motor to continue its rotation causing opening of the second contact at the end of the heating sequence, this cycle being repeated automatically when the second contact is closed afresh at the commencement of the following heating sequence.
Thus it is understood that if no flame is detected at the burner by the flame presence security device, the reversing contact of this safety device remains in a second position in which the electric feed of the motor is cut off and the burner gas feed electric valve is closed, as soon as the first contact is opened by the cam fixed to the drum.
Under these conditions the safety system automatically avoids all risk of gas escape as a consequence of a prolonged supply of gas to the burner while the latter is extinguished.
Further particular features and advantages of the invention will appear in the course of the following description. Two forms of embodiment of the invention are represented in the accompanying drawings, given by way of non-limitative examples.